In many types of equipment that use movements of air or other gases, measuring the mass flow rate of the gas and/or static gas pressure is very important. An example is a HVAC system of a residential dwelling that incorporates an air filter. Typically, mass of gas (air, in particular) is driven through the dwelling or machinery by means of a forced convection. The purpose of the air filters is to remove airborne contaminants that may adversely effect health of humans and animals, cause malfunction or reduction in efficiency of equipment, and deposits of soiling compounds onto various surfaces. A typical HVAC system is shown in FIG. 1 where the house 1 has generally atmospheric pressure P2 due to exposure to atmosphere through doors and windows 80. The HVAC system is comprised of the blower 5, air conditioner/burner 6, and air filter 7. The blower 5 moves air. The air flow 2 is indicated by arrows. The static negative air pressures (as compared to the atmosphere) are formed across the air filter 7, adjacent to it sides 8 and 9. These pressures cause the air flow 2 through the filter and through the air duct 4 connected to the house. The negative air pressures at sides 8 and 9 are shown in FIG. 2 and the air flow rate is shown in FIG. 3 as function of the air filter 7 clogging, in percents, where a 100% clogging is a total filter blockage. It is clear from FIGS. 2 and 3 that the filter contamination can be detected either from monitoring the air flow rate or from one or both static air pressures across the filter 7. To detect the air filter clogging in a HVAC system, the monitor 10 with a sensor 11 can be installed into an air duct either upstream or downstream from the air filter 7. Note that the sensor 11 can be either a flow sensor or pressure sensor.
In the automotive applications and various types of fuel burners, providing a right fuel-to-air ratio is critical for the device efficiency and reduction of pollution. In these devices monitoring either a pressure at the blower or air flow can be very beneficial.
In medical equipment used for anesthesiology, gases should be efficiently mixed for safety and correct medical effect. A flow monitoring is an important part of the gas delivery control system.
In security systems, one method of detecting an intrusion into a protected area is monitoring variations in air pressure that may result from closing and opening of doors and window. All the above requires monitoring of very low changes in air pressure and inexpensive and safe monitoring of the air mass flow rate.
In this patent, we use word “air”, although it should be understood that any gas or mixture of gases can be monitored in a similar manner.